Overheating problem or normal?

[Jared1048]

I've recently bought a 1985 Hunter 31 (2GM20F) and I've had to kill the motor (twice) due to the alarm going off.

After the first time I replaced the mixing elbow due to a pin hole leak.

Now its overheated for the second time while running at about 3300 rpm for about 30 minutes.

Would this be expected or do you think there is another hidrance to the cooling system somewhere?


Thanks!
-Jared

 

[Steve Dion]

Jared:

Do you know which prop you have on the boat? Some of the original props were over-proped.

I assume you have checked the raw water intake and impeller. You may also need to check the heat exchanger too. You can get buildup or growth in there. Be sure that your strainer is clean and none of your hoses on the raw water intake side are collapsing.

3300 is running the engine at higher than normal RPM. The NORMAL cruising range on the 2GM is approx. 2600 - 3000 rpm.

 

[Jared1048]

The prop is listed as, "15 RH 12 two-bladed bronze" from the survey. It also mentions, "Reduction Gear: Kanzaki KM2C 2.62:1".

I haven’t checked anything yet. The water intake thru hull was just replaced along with the driveshaft and cutlass bearing if that matters at all.


Thanks for the quick reply!
-Jared

 

[Dan Johnson]

Check...

to see if you have a strainer in the intake line that could have become clogged. Next check the flow out of the thru-hull.

I picked up some sort of trash last year that caused an overheat alarm for the first time ever. There was no water coming out of the intake thru-hull when I took the hose off and opened the valve. Used compressed air to blow it out and got underway again in minutes-3 hours more at 2,800 RPM without a beep and no problem since.

 

[Neil McDonald]

I've recently bought a 1985 Hunter 31 (2GM20F) and I've had to kill the motor (twice) due to the alarm going off.

After the first time I replaced the mixing elbow due to a pin hole leak.

Now its overheated for the second time while running at about 3300 rpm for about 30 minutes.

Would this be expected or do you think there is another hidrance to the cooling system somewhere?


Thanks!
-Jared

You may be stressing the cooling system by excessive rpm. If I recall correctly Yanmars are happiest at about 70% of max rated rpm, which should put you under 3,000 rpm.

Pull hose off back of heat exchanger and briefly run engine. Water should really squirt out strongly if all is well!

If not, check though-hull, then water strainer, then replace water pump impeller.......... even if not damaged. Chances are that it has not been replaced recently.

Check that there are no bits of old impeller stuck in the tube to the heat exchanger or on the face of heat exchanger tubes. Pull front and back plate of heat exchanger plate and clean tubes with stiff wire or better still a small bore rifle brush.

Good luck.

 

[Rich M]

I also have a 1985 2GM in a 28.5. What I have found is that at those rpm and the resulting speed the actual amount of water coming in to cool the engine is significantly reduced. I also think you are stressing the system a bit.

 

[Steve Dion]

Jared:

Check with a local prop shop to see what they say. We had a 15 x12 on our H'31 and experienced overheating at higher RPM's also.

We went to a 15 x 10 with much better results.

Remember that these tach's are not always correct, so you may want to check that out too before you invest any more time/effort into something that may not be totally correct.

 

[Scott]

check your water pump belt.

 

[Jared1048]

So I cracked open the sea strainer and found it to be extremely dirty. I blasted it with a hose and had to clean up about a handful of small rocks. The filter itself had algae growing all over it.

With that cleaned up the water output was noticeably increased.

Im going to replace the impellor also but it didnt look as easy.


Thanks!
-Jared

 

[sailnteacher77]

If that does not do the trick. Check your coolant circulation pump. The engine will run for 30 minutes perfectly just on fresh seawater and hot coolant, bu the party is over if the coolant iant circulating. If it has this pump, its only about 140 for a new one, compared with the seawater pump replacement cost, its pretty light.